1. Field of the Invention
The present invention generally relates to an apparatus and method for securing a wafer to a support assembly and, more particularly to a method and apparatus for securing a wafer to a support assembly to provide a wedging action between the wafer and the support assembly.
2. Background of the Related Art
Sub-quarter micron, multi-level metallization is an important technology for the next generation of ultra large scale integration (ULSI). As circuit densities increase as a result of technological progress, the widths of these circuit features, as well as the width of the dielectric materials between the features, decrease considerably. However, the height of the dielectric layers remains substantially constant. Therefore, the aspect ratios of the features (i.e., their height divided by width) increase. A great amount of ongoing effort is directed at the formation of void-free, nanometer-sized circuits including features having aspect ratios of 4:1, or higher.
One process and system gaining acceptance for filling small features with copper is electroplating (ECP) and related processes. ECP is a wet process and requires rinsing and drying steps that follow the ECP process. One device commonly associated with electroplating and other wet processes to accomplish the rinsing and drying of the substrate is a spin-rinse-dry (SRD) unit. Wafers undergoing a SRD cycle are secured to a cross member referred to as a SRD holder (usually in a face-up position) by a plurality of wafer clips which are mounted on the SRD unit.
The SRD unit performs a SRD cycle on a wafer; the SRD cycle comprises a rinse cycle followed by a dry cycle. Alternatively in a SRD cycle, the rinse cycles may be alternated with the dry cycles. The SRD unit rotates the SRD holder (and a wafer contained therein) at a high angular velocity subjecting the wafer to relatively high accelerations. SRD units may change angular rotational direction of the SRD holder between a clockwise and a counter-clockwise direction during both the rinse cycle and the dry cycle. The changing of angular rotational directions by the SRD holder applies further centrifugal accelerations to the wafer that enhances the drying characteristics of the SRD unit. During the rinse cycle, a surface of the wafer supported by the SRD holder is sprayed with cleaning or rinsing fluids to facilitate removal of unwanted material from the surface of the substrate. During the dry cycle, the angular rotation imparted to a wafer supported by the SRD holder effectively dries the wafer through the combined action of centrifugal forces and air flow.
However, the wafer may become wedged in position in a SRD holder because of the angular rotations of the SRD holder about a vertical axis during the SRD cycle. Robot manipulators follow mechanical robot motions such as lifting, rotating, etc. In lifting the wafer by the robot manipulator, the upward force of the robot end effector or blade on the bottom of the wafer to lift the wafer has to overcome the wedging force. When a considerable amount of lifting force is applied upwardly to the wafer to dislodge the wafer from between the posts of the SRD holder, and a considerable wedging force is generated, the wafer may build up potential energy. This potential energy is demonstrated by bowing of the wafer, and the wafer may spring out of the SRD holder and become damaged or mis-oriented as the wafer springs from the SRD holder. The upward force applied to the wafer as the wafer is held in the wafer""s wedged position may also break the wafer.
Therefore, there is a need for a clip arrangement that securely wafers to the SRD unit in a manner that limits the wedging force that exists between the wafer and the SRD holder. Reducing the wedging force would also reduce the force necessary to remove the wafer from the SRD holder.
The present invention generally relates to a SRD unit. In one aspect, an apparatus and associated method is described for securing a wafer to a SRD holder. The SRD holder has a plurality of arms. The apparatus includes a plurality of spaced surfaces disposed on a distal end of one of the arms, each of the surfaces being spaced perpendicularly from the longitudinal axis of the arm. In one aspect, the two surfaces are positioned to limit production of a wedging force between the spaced surface and the wafer. In one embodiment, a post at least partially defines each one of the plurality of spaced surfaces.